Cathode-ray tube including a glass envelope with two spaced external conductive coating and a connecting strip of a third external conductive coating thereon

ABSTRACT

A cathode-ray tube including a glass envelope having a forward portion terminating in a viewing screen, a center portion, and a rear portion including an electron-gun assembly having at least one focusing lens therein. A first external conductive coating is on the forward portion of the envelope, and a second conductive coating spaced from the first conductive coating is on the rear portion of the envelope at least over the focusing lens. A longitudinal strip of a third external conductive coating on the center portion of the envelope connects the first and second conductive coatings.

[ CATIIODE-RAY TUBE INCLUDING A GLASS ENVELOPE WITH TWO SPACED EXTERNALCONDUCTIVE COATING AND A CONNECTING STRIP OF A THIRD EXTERNAL CONDUCTIVECOATING 7/1952 Breeden 313/85 R X 2,771,566 11/1956 Baracket 313/85 R X2,829,292 4/1958 Krause 313/85 R X 3,614,519 10/1971 Figlewicz 313/85 SX FOREIGN PATENTS OR APPLICATIONS 6,703,723 9/1967 Netherlands 313/85 RPrimary Examiner-Robert Segal AttorneyGlenn H. Brustle [57] ABSTRACT Acathode-ray tube including a glass envelope having a forward portionterminating in a viewing screen, a center portion, and a rear portionincluding an electron-gun assembly having at least one focusing lenstherein. A first external conductive coating is on the forward portionof the envelope, and a second conductive coating spaced from the firstconductive coating is on the rear portion of the envelope at least overthe focusing lens. A longitudinal strip of a third external conductivecoating on the center portion of the envelope connects the first andsecond conductive coatings.

1 Claim, 1 Drawing Figure Patented July 17, 1973 3,746,904

' INVEN'IOR. ALTON J. TORRE ATTORNEY CATHODE-RAY TUBE INCLUDING A CLASSENVELOPE WITH TWO SPACED EXTERNAL CONDUCTIVE COATING AND A CONNECTINGSTRIP OF A THIRD EXTERNAL CONDUCTIVE COATING THEREON BACKGROUND OF THEINVENTION The invention relates to a novel cathode-ray tube, forexample, to a color television picture tube, including a glass envelopewith two spaced external conductive coatings and a connecting strip of athird conductive coating thereon.

One type of cathode-ray tube conventionally comprises a glass envelopehaving a forward portion terminating in a vewing window with aluminescent viewing screen thereon and a rear portion includingbipotential electron-gun assembly having at least one electron gun withfocusing lens. Each electron gun projects one electron beam towards thewindow to excite the screen to luminescence. A deflection yoke mountedon the envelope includes magnetic field producing coils positionedadjacent the envelope to provide for deflection of the electron beams.

The tube includes a first external conductive coating on the forwardportion of the envelope or funnel between the yoke and the viewingscreen and a second conductive coating, spaced from the first conductivecoating, on the rear portion of the envelope or neck at least over thefocusing lenses of the electron gun. The second conductive coating isspaced from the first coating to permit mounting of the yoke on anuncoated portion of the envelope. If the yoke were mounted on aconductive coating, it may accidentally become grounded to the coating.In the operation of the tube, the second coating is connected to aground potential with a spring clip clamped against the coating, whichis in turn connected with a ground wire to a convenient groundpotential. By grounding the second coating in this manner, a specialclip with groundwire is necessary, which increases the cost of equipmentnecessary for tube operation. In addition, the clip with ground wireresults in an increased number of separate external componentsnecessaryfor tube operation. Furthermore, the ground clip may becomeeasily disconnected or may be improperly connected, resulting indecreased operating performance of the tube.

SUMMARY OF THE INVENTION As in the prior art, the novel cathode-ray tubeincludes an evacuated glass envelope having a forward portion or funnelterminating in a viewing screen, a center portion, and a rear portion orneck including an electron gun therein. The forward portion includes afirst external conductive coating, and the rear portion includes asecond external conductive coating, spaced from the first externalconductive coating, at least around the envelope over the focusing lensof the electron gun. Unlike the prior art, the center portion includes alongitudinal strip of a third external conductive coating connecting thefirst and second coatings.

In operation, a deflection yoke having two pair of magnetic fieldproducing coils, each coil having a window, is mounted on the centerportion of the novel tube. The yoke is positioned over the centerportion with at least one of the windows formed by the inner pair ofcoils positioned over the strip. The novel tube eliminates the clip withground wire and utilizes an external strip of conductive coating toconnect the second coating to the first coating. The connecting stripconnects the second coating to ground potential since the first coatingis normally connected to a ground potential during the use of the tube.Since the first, second and connecting strip of a third conductivecoating can be simultaneously applied using existing processes at a costsubstantially equal to the cost of only the additional coating material,and the clip with ground wire is eliminated, an economy results in themanufacture and use of the novel tube. In addition, the elimination ofthe clip with ground wire reduces the number of separate externalcomponents required for the operation of the tube. Furthermore,replacing the separate mechanical ground connection with an integralground connection in the form of a strip of conductive coating providesmore assurance that the second coating is always connected to groundpotential during the operation of the tube. Also, the novel tube can beinstalled in equipment not previously provided with a mechanical ground,thereby resulting in increased tubeoperating performance withoutrequiring a receiver modification.

BRIEF DESCRIPTION OF THE DRAWING The sole FIGURE is a partially brokenaway top elevational view of the novel color television picture tube andassociated magnetic deflection yoke illustrating the external strip ofconducting coating thereon.

DESCRIPTION OF THE PREFERRED EMBODIMENT The novel color televisionpicture tube 10 with an electromagnetic deflection yoke 11 positionedthereon is illustrated in the sole FIGURE. The tube 10 comprises a glassenvelope 12 including a forward portion or funnel 13 terminating in apanel 14 having a viewing window 15, a rear portion or neck 16terminating in a stem assembly 17, and a flared center portion 18connecting between the funnel l3 and neck 16. The inside surface of thefunnl 13'includes an internal conductive coating 19. An anode connection20 is provided through the funnel 13 for connecting a high voltage tothe internal coating 19. A luminescent viewing screen 21 comprised of amultiplicity of phosphor dots is supported on the inside surface of theviewing window 15, and an aperture-mask assembly 22 is positioned in theenvelope in front of the screen 21. An electron-gun assembly 23 ispositioned in the neck 16 for projecting three electron beams 24 red(r), blue (b), and green (g) towards the aperture-mask assembly 22 andthe screen 21.

The electron-gun assembly 23 includes three electron guns 25 (only oneof which is partially shown in the sole FIGURE). The electron-gunassembly 23 includes a first grid G-l (not shown), a second grid G-2(not shown), a third or focusing grid G-3 designated 26, and a fourthgrid or anode G-4 designated 27. A convergence assembly 28 is coupled tothe three electron guns 25. A spacing B exists between the third andfourth grids 26 and 27. The third grid 26 is at approximately 5,500volts, and the fourth grid 27 is at approximately 25,000 volts. Thespacing B" and potential difference produce a lens-like configuration ofequipotential field lines resulting in the formation of one of the threeelectron beams 24. The lens-like configuration having the spacing B" istherefore generally designated a focusing lens of one of the threeelectron guns 25. For an electron-gun assembly 23 comprising threeelectron guns 25, there are three focusing lenses 29 in substantialalignment.

The tube includes a first external conductive coating 30 on the externalsurface of the funnel 13. The first external coating 30 coverssubstantially the entire external surface of the funnel 13 except for anarea surrounding the anode connection 20. This is to prevent currentleakage from the anode connection to the first external coating 30. Theinternal conductive coating 19, the glass funnel l3, and the firstexternal conductive coating in combination provide voltage regulation inthe operation of a color television receiver, as is known.

The tube 10 also includes a second external conductive coating 31 on theneck 16. In the preferred embodiment, the second external coating 31comprises a band around the neck 16 positioned substantially centeredover the focusing lenses 29 of the electron-gun assembly 23. The secondexternal coating 31 is believed to equally distribute electrical chargesaccumulating on the inner surface of the neck 16 over the focusinglenses 29, thereby reducing convergence shift of the electron beams 24caused by the prior nonuniform charge distribution. Referring to thesole FIGURE, it is preferred the the band of second external coating 31is approximately 0.75-inch wide.

A longitudinal strip of a third external conductive coating 32 on thecenter portion 18 of the envelope 12 parallel to the axis A-A of thetube 10 connects the first and second external coatings 30 and 31respectively. In the preferred embodiment, the third external coating 32is a longitudinal strip on the top of the surface of the envelope 12approximately 0.25-inch wide. In this description, the top of theenvelope 12 is defined to be that portion of the envelope which isuppermost when positioned in a television receiver.

In the opeation of the novel tube 10, an electromagnetic deflection yoke11 of the well-known saddle type is positioned on the envelope 12adjacent the center portion 18 of the envelope 12. The yoke 11 isconventionally positioned on the envelope to produce a deflection fieldfor deflecting the electron beams 24 from the electron-gun assembly 23to horizontally and vertically sweep the screen 21 scanning arectangular raster at the screen 21 in a known manner. The yoke 11includes a set of saddle-type vertical deflection coils 33 and a set ofsaddle-type horizontal deflection coils 34. The usual convention is toposition the horizontal deflection coils 34 inside the verticaldeflection coils 33 and in close proximity to the envelope 12.

The horizontal coils 34 each have two spaced groups of active sideconductors 35 and 36 extending generally along the longitudinal axis A-Aof the tube 10 (only one coil is shown in the sole FIGURE) and spacedfrom one another circumferentially of the tube 10. The spaced groups ofside conductors 35 and 36 are joined at their ends by groups ofconnecting front and rear end conductors 37 and 38 respectivelyextending traversely of the tube 10. The groups of side conductors 35and 36 follow the contour of the envelope 12 on the center portion 18,flaring up at their ends to join the groups of front and rear endconductors 37 and 38, which are spaced from the tube 10. The groups offront and rear end conductors 37 and 38 are usually flared up and spacedfrom the envelope 12 to prevent their generating a field which interactswith the desired deflection field. The open center space between the twospaced groups of side conductors 35 and 36 and the connecting groups offront and rear end conductors 37 and 38 is generally defined to be awindow 39.

It is preferred that the longitudinal strip ofa third external coating32 which is positioned on the center portion 18 of the envelope 12 notcontact or be positioned under the two spaced groups of side conductors35 and 36 of the horizontal coils 34 to prevent grounding of the thirdexternal coating 32 by the shorting of the insulation on the coils.

In the preferred embodiment, the third external coating 32 is on thetube 10 substantially centered under one window 39 between the twospaced groups of side conductors 35 and 36 (shown in the sole FIGURE)when the yoke 11 is positioned on the tube 10. The width C of the stripof third external coating 32 should not exceed the width of thenarrowest portion of the window 39. If the width C of the strip of thirdexternal coating 32 is greater than the narrowest width D of the window,it would be under and in contact with the horizontal coil 34, which aspreviously described, is not desirable.

In the operation of the tube 10 with yoke 11, one window 39 formed byone of the horizontal coils 34 is centered over the top of the envelopel2, and the other window (not shown) formed by the other horizontal coil(not shown) is positioned opposed from the first window 39 centered overthe bottom of the envelope 12. In a 25VABP22 color television picturetube, the anode connection 20 is located on the bottom of the funnel 13.Since the third external coating 32 does not extend near the anodeconnection 20 as previously described, a longitudinal strip of a thirdexternal coating 32 would not directly connect with the first externalcoating 30. It is therefore preferred that the third external conductivecoating 32 be positioned under the window 39 on the top of the envelope12 as previously described.

The first, second and third external coatings 30, 31 and 32 respectivelyare deposited from a colloidal graphite suspension such as, for example,Aquadag." It is preferred that the dry coatings are about 0.001- inchthick and have a low resistance such as, for example, ohms per linearinch. It is preferred that the coatings are applied as one continuouslayer of suspension, rather than as separate abutting or overlappinglayers, to provide uniform thickness and resistance.

The coatings are preferably applied by spraying, which is well known.

In the preferred method of applying the coatings, a spray shield (notshown) is positioned over the envelope 12. The shield closely fitsagainst and substantially conforms to the contour of the envelope 12.The shield has cutouts or openings over the portions of the envelope 12corresponding to the desired position of the coatings 30, 31 and 32 onthe envelope 12. The coatings are then applied by spraying onto theunshielded portions of the envelope 12.

Although, in the preferred embodiment, the third external coating 32 isa strip about 0.25 inch wide, the coating width may be narrower sincethere is substantially no current flow in the coating, The onlyrequirement is that the coating width be sufficient to maintain thesecond coating 31 at ground potential.

Although the third external coating 32 is described as a strip of auniform width, it may be of varying width limited only by the width ofthe window 39 as previously described.

Although particular shapes for the first and second coatings 30 and 31respectively are described in the preferred embodiment, other shapes canbe used such as, for example, the second coating may cover the entiresurface of the neck 16.

Although it is described that the horizontal coils 34 are positioned incontact with the envelope 12 and contain a window 39 under which thethird conductive coating 32 can be positioned without contacting thespaced groups of side conductors 34 and 36, the vertical coils 33 mayalternatively be positioned in contact with the envelope 12. Thevertical coils 33 are similar to the horizontal coils 34 and similarlycontain a window which would be positioned over the sides of the tubeand under which the third conductive coating 32 can be positionedwithout contacting spaced groups of side conductors of the verticalcoils 33.

I claim:

1. In combination, a cathode-ray tube including a glass envelope havinga forward conical portion terminating in a viewing window, a center yokereceiving portion, and a rear neck portion having therein a plurality ofelectron guns in a delta array, each of said guns having a focusinglens, said tube comprising a. a first conductive coating substantiallycovering the external surface of said conical portion, except for aportion surrounding the anode connection, b. a second circumferentialband of conductive coating on the external surface of said neck portionsubstantially centered over said focusing lenses of said electron guns,and c. a longitudinal strip of a third conductive coating on theexternal surface of said yoke receiving portion of said envelopeconnecting said first coating and said second coating; and a saddle yokecomprising at least two inner opposed magnetic field producing coils,each coil having a window which is formed by two spaced groups of sideconductors and two connecting groups of end conductors, said yoke beingpositioned over said yoke receiving portion, with at least one of thewindows formed by the inner pair of coils positioned over said strip,said longitudinal strip being of a width less than the space between thetwo spaced groups of side conductors forming one of said two windows andcapable of maintaining said first and said second conductiv'e coatingsat the same potential.

1. In combination, a cathode-ray tube including a glass envelope havinga forward conical portion terminating in a viewing window, a center yokereceiving portion, and a rear neck portion having therein a plurality ofelectron guns in a delta array, each of said guns having a focusinglens, said tube comprising a. a first conductive coating substantiallycovering the external surface of said conical portion, except for aportion surrounding the anode connection, b. a second circumferentialband of conductive coating on the external surface of said neck portionsubstantially centered over said focusing lenses of said electron guns,and c. a longitudinal strip of a third conductive coating on theexternal surface of said yoke receiving portion of said envelopeconnecting said first coating and said second coating; and a saddle yokecomprising at least two inner opposed magnetic field producing coils,each coil having a window which is formed by two spaced groups of sideconductors and two connecting groups of end conductors, said yoke beingpositioned over said yoke receiving portion, with at least one of thewindows formed by the inner pair of coils positioned over said strip,said longitudinal strip being of a width less than the space between thetwo spaced groups of side conductors forming one of said two windows andcapable of maintaining said first and said second conductive coatings atthe same potential.